For many years, little attention was directed to the preservation of the earth's environment and its natural resources, particularly its limited mineral resources. It generally was considered more economically feasible to mine metal ores and simply dump rich metal-bearing wastes into landfills, rather than to recover and recycle usable metals and other products from industrial waste materials, particularly those industrial wastes containing hazardous or toxic materials.
Public concern over environmental issues, particularly the disposal of hazardous wastes, the decreasing availability of landfill areas, and the continuing depletion of the earth's mineral resources, has risen significantly over the last decade. Additionally, economic pressures and the tightening of competition for the earth's natural resources have increased. Further, federal and state regulations regarding the use of the earth's natural resources and the disposal of hazardous waste materials have become more encompassing and more restrictive. As a result, industry has begun to take appropriate and decisive measures in order to minimize waste. One focus of scientific undertaking in this area has been the recycling of industrial wastes and the recovery and reuse of all commercially useful byproducts derived from industrial processes.
One prior approach commonly used in the disposal of industrial wastes, particularly hazardous industrial wastes, is to "stabilize" or "capture" the waste material in a generally non-leachable form, typically with a basic material, such as lime or cement. Such stabilized waste materials subsequently are buried in designated hazardous waste landfills. Another widely accepted technique for the disposal method of hazardous wastes is to incorporate these waste products into a glass-like matrix commonly referred to as a "slag". This "slag" typically was used as a substitute for natural rock aggregate in cement or asphalt compositions utilized in the paving of roads and the like.
The United States Environmental Protection Agency (EPA), as directed by, for example, the Resource Conservation and Recovery Act (RCRA) and the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), defines and classifies certain wastes materials for controlled disposal. Moreover, the manner in which wastes materials are treated also are covered by EPA regulations. For example, the ultimate end use of the treated waste material, generally referred to as a secondary material, determines whether it still is within the definition of "solid waste" (and, therefore, a hazardous waste). The regulations include in the definition of "solid waste", those waste materials which have been diluted, treated or otherwise stabilized. More specifically, the regulations provide that secondary materials and products containing secondary materials, when applied to or placed on the land in a manner that constitutes disposal, continue to be defined as "solid waste" and also hazardous waste [.sctn.261.2(e) of RCRA]. In other words, waste materials which have been diluted, treated or otherwise stabilized, simply cannot be disposed or used as a replacement for any product which is typically used on the land in any form, but rather, are subject to EPA restrictions relating to solid/hazardous waste management. Consequently, the waste materials treated in the above-discussed methods continue to be defined as hazardous wastes, and, as a result, the methods discussed above have fallen into disfavor.
The EPA has developed a series of questions called "the recycling criteria" in order to analyze individual recycling operations and determine whether the operation is legitimate recycling or "sham" recycling. The difference is that legitimate recycling involves an economic benefit from the recycling of wastes while "sham" recycling evades proper hazardous waste management. Am economic benefit includes, for example, recycling the hazardous waste materials and extracting products of known commercial value. The "criteria" regulation further requires that the recycler must possess a demonstration of legitimate recycling known as the "burden of proof". If the recycler does not possess an adequate demonstration, then the default presumption is that the operation is "sham" recycling. When a waste material has been recycled legitimately, products derived therefrom are not considered a solid waste under RCRA, that is, such products are not used in a manner constituting disposal. In other words, products recovered from waste materials by legitimate recycling methods are not subject to RCRA permitting requirements for disposal. Such products include, for example, metals, metal alloys, metal oxides, slag-based products such as mineral wool, abrasives and glass frits for use in roofing granules, glass ceramics or ceramic glaze/colorants.
The United States Environmental Protective Agency presently categorizes a number of waste material by the following designated series: D, F, K, P and U. Many waste materials are not classified as being hazardous wastes, although it is expected that the list of classified hazardous wastes will enlarge with time. Currently, a substantial number of waste products, generally recognized as unsafe for conventional disposal, are not yet under EPA scrutiny and restrictions. For example, certain anodizing wastes, such as EPA designated waste F019, are presently listed as wastes, but not classified as hazardous wastes. Further, sand used in blasting operations which may be contaminated with nickel, chrome, or other metals generally considered toxic, and baghouse dusts which often contain carbon and hazardous materials, have no separate classification under the current law. Consequently, such wastes are discarded without meaningful disposal precautions, despite the fact that they are widely believed to create hazards to the environment. Moreover, their disposal results in the unnecessary depletion of existing natural mineral resources.
There are numerous methods for disposing of wastes materials, particularly hazardous waste materials, currently known and practiced in the prior art. For example, U.S. Pat. No. 4,432,666 to Frey describes a process for storing and dumping hazardous wastes. U.S. Pat. No. 4,793,933 to Rostoker teaches a method for treating metal hydroxide electroplating sludges by fusion of the oxides of the metals into silica and sodium slag. The Rostoker method relates to earlier EP Leaching standards and has been proven incapable of achieving minimal-waste recycling. U.S. Pat. No. 4,480,671 to Lynn relates to the stabilization of EAF dusts for disposal by use of calcium hydroxides as entrapping agents for toxic cadmium, chromium, and lead constituents. Lynn suggests combining and processing various and distinct waste products in order to produce "safe" compounds.
The prior art also is replete with methods for producing useful commercial products from various industry wastes. Such products include furnace fuels, paving aggregates, sealing compounds, and mineral wool.
Mineral wool is a term broadly applied to various related vitreous products commonly used for insulation, padding, ceiling tile production, and the like. In general, mineral wool is a fiberglass-like material composed of very fine, interlaced mineral fibers, somewhat similar in appearance to loose wool. It is composed primarily of silicates of calcium and aluminum, chromium, titanium, and zirconium. Typically, mineral wool is produced from natural rock or slag. Slag is a term broadly applied to refer to waste products of the primary metal and foundry industries, including deposits from the furnace lining charge impurities, ash from fuel, and fluxes used to clean the furnace and remove impurities. Although metal producers and foundries strive to control the amount of slag, excess slag may result from the refining of metals.
Slags are classified as either "acid" (i.e. high silicate) slags or "basic" slags, depending upon the relative quantities of acidic and basic sub-components. For example, typical acid slags contain between forty and fifty percent (40.0 to 50.0%) of acidic subcomponents, such as silicon dioxide (SiO.sub.2), from twenty-five to forty-five percent (25.0 to 45.0%) of basic sub-components, such as the oxides of calcium (CaO) and magnesium (MgO), and from ten to twenty percent (10 to 20%) of alumina Al.sub.2 O.sub.3. A typical basic slag that is used to reilne or reduce metals comprises between twenty-five and fifty percent (25.0 to 50.0%) acidic subcomponents such as silicon dioxide (SiO.sub.2) and alumina (A1.sub.2 O.sub.3), and a relatively high percentage, between thirty-four and fifty percent (34.0 to 50.0%) basic subcomponents, such as the oxides of calcium (CaO) and magnesium (MgO). Magnesium may be added to increase the basicity of the slag. Basicity is the tool used to determine the metal quality using basic slag. Basicity is calculated as follows: CaO+Mgo/Al.sub.2 O.sub.3 +SiO.sub.2. The basicity of typical basic slags ranges between 0.93 and 1.9.
Typically, metal producers are interested in the highest quality metals with the least amount of slag production since traditionally it is expensive to melt slag, and the slag is of little value or it is an environmental liability. Because high quality scrap metal is abundant, modem metal producers prefer to use acid slags and not refine metals. For premium results, mineral wool producers seek slags or rock that can be blended together and melted at relatively low temperatures. Preferable the mineral wool slag will contain no reducible metals, or will be an acid slag that will eliminate metal buildup in the furnace.
Mineral wool is classified according to the raw materials used in its production. For example, Rock Wool is produced from combinations of natural rocks and/or minerals. Slag Wool comprises a composition of iron, copper and lead slags typically removed from blast furnaces, and may contain some fluxing materials. Glass Wool (fiberglass) is composed principally of silica sand, soda ash, and limestone, Refractory (high-temperature) or "Certa" wools may be made from the oxides of aluminum, chromium, zirconium, or titanium and silica sand. Further subclassifications of these products relate to the quality or purity of the wool. For example, slag wool is subclassified for purity according to color: black, gray, and white wools are available. The tool for determining the quality of mineral wool produced from a slag charge is the acid-to-base ratio (A:B). The formula for determining A:B is Al.sub.2 O.sub.3 +SiO.sub.2 / CaO+MgO. In a typical mineral wool derived from cupola slag, the acid-to-base ratio ranges between 0.74 and 2.316.
Prior art patents relating to the production of mineral wool using various waste products include U.S. Pat. No. 4,822,388 to Gee and U.S. Pat. No. 4,484,211 to Monaghan. Monaghan discloses a method and apparatus for melting discarded fly ash and spinning it into mineral wool. However, non of the prior art known to us teaches viable methods for recycling EPA designated wastes, particularly hazardous materials, containing waste metal oxides such as chromium, nickel, cadmium, zinc, copper, iron, and lead oxides or hydroxides, into pure metals or alloys while producing mineral wools from non-reducible metal oxides, such as the oxides of aluminum, silica, calcium, zirconium, and titanium.
Methods for the treatment, recovery and recycling of waste materials also are well known in the prior art. For instance, U.S. Pat. No. 3,870,507 to Allen is directed to a method for forming briquettes from steel mill wastes (such as steel and iron dust, mill scale and iron oxides) with an organic binder, in order to reduce slags formed during recycling. The resulting iron oxide briquettes are recycled by being fed into the production furnaces with new materials in the steel-making process.
U.S. Pat. No. 4,004,918 to Fukoka teaches a method for treating certain wastes resulting from stainless steel operations. In Fukoka, briquettes are formed from the dust and scale from stainless steel ovens and combined with organic and inorganic binders. The briquettes are returned to the existing electric are furnace, and usable metals are extracted for further use in making stainless steel.
U.S. Pat. Nos. 4,053,301 and 4,396,423 to Stephens relate to a process for the recovery of iron carbide and zinc metals from BOF dusts resulting in the steel-making process. The Stephen's system reduces the dust wastes within a fluidized bed reactor in the presence of carbon, recovers zinc by vaporization, and produces iron carbide and gangue, a worthless rock or matter in which metals are contained.
U.S. Pat. Nos. 4,758,268 and 4,836,847 to Bishop disclose apparatus and processes for reclaiming metals from electric arc furnace and BOF dusts. The systems described therein are directed to providing recovery of metals from EAF wastes in a reducing environment. In the Bishop method, carbon is added to the molded briquettes to reduce the iron and zinc content of the waste. However, the process is incapable of producing a slag suitable for use in the production of mineral wool, since the process attempts to minimize slags to less than 8%. Moreover, the Bishop system specifically is described as being unsuited for rotary kilns, shaft fumaces, retorts, and fluidized bed furnaces.
Despite the many treatment and recycling processes known in the prior art and discussed above, a need still exists for providing a method of legitimate recycling, wherein industrial waste materials, including hazardous waste materials, can be effectively recycled in such a manner that the waste material is consumed and as much usable material as possible is recovered and convened to viable commercial products. Such a method must effectively eliminate waste, conserve natural resources and avoid costly liability. Moreover, such a process should be capable of being carried out with equipment and apparatus already available in the industry.